Along with endoscopes for medical and non-medical technical applications, whose viewing angle is parallel to the longitudinal axis of the endoscope shaft, endoscopes with other fixed viewing angles were developed from an early date. Here and throughout the present document, the viewing angle of an endoscope is always understood to mean the direction looking outward from the distal end of the endoscope, that is, the direction in which an object is situated that appears in the center of the image recorded by means of the endoscope. With many applications, however, a fixed viewing angle is a disadvantage. In the most unfavorable case, for example, the endoscope must be replaced repeatedly during a medical procedure. In such cases it is advantageous to use an endoscope with a viewing angle that can be adjusted and/or displaced in situ.
A swing prism endoscope comprises on its distal end a pivotable prism on whose border surfaces light falling into the endoscope is refracted and reflected before it is conveyed, by means of a rod lens system for example, to the proximal end of the endoscope. By pivoting the prism around an axis perpendicular to the longitudinal axis of the endoscope shaft, the viewing angle can be adjusted.
In conventional swing prism endoscopes, the viewing angle range, instantaneous field of view, brightness and image quality are often unsatisfactory. If the viewing angle range is intended to include a viewing direction parallel to the axis of the endoscope shaft (0 degree), for a long time it was only possible to achieve a small viewing angle range. To date, it was not possible to achieve a large viewing angle range whose extreme viewing angles encompass 120 degrees or more.
Patent DE 600 15 375 T2 describes an endoscope with variable viewing angle, which includes two right-angle prisms. One of the right-angle prisms can rotate about an axis of rotation that is orthogonal to the longitudinal axis of the endoscope and intersects it.